At the beginning switch off your mobile phone by holding down the Power rocker for a short while.Afterwards press and hold together: Volume Up + Home + Power button for a couple of seconds.When the Samsung Logo appears, you can release held keys.In the next step select from menu "wipe data / factory reset" using Volume buttons to navigate and Home button to confirmChoose "Yes -- delete all user data" to confirm the whole operation.After that select option "reboot system now".Well done! The hard reset has just been performed.

OR

Start by turninng on the device.From the Home Screen go to Menu and then to Settings.Tap Backup & Reset and then Factory data reset.Afterwards choose Reset device.To confirm your choice select Erase everything.That's all.